1. Field of the Invention
The present invention relates to a method for evaluating pattern formation processes and a photomask for the evaluation, specifically to a method for evaluating pattern formation processes applied primarily to the analysis of variations in line-width during an exposure process, a photoresist process, a dry-etching process, etc. in manufacturing semiconductor devices and a photomask for the evaluation.
2. Description of the Related Art
Recently, various effects of the periphery around the pattern concerned has been a problem in a pattern formation process for semiconductor devices having fine integrated structure particularly of the order of sub-micron.
For example, when there is a large region without any patterns in the vicinity of the fine patterns concerned, and especially when the region is a transparent region formed by the exposure of light transmitted in a photolithography process, the variations in dimension of the fine patterns due to micro-flare at the time of exposure has been a problem.
Referring now to FIGS. 14A and 14B the phenomenon of the micro-flare above will be briefly described. FIG. 14A shows part of a reticule on which patterns of a device are drawn. In this simplified example, the patterns of the device are an arrangement of a plurality of line patterns 11 having a line-width and an interval less than or on the order of sub-micron. As shown in FIG. 14B, it is a frequently observed phenomenon in a photoresist pattern after light exposure that a line-width of each line pattern 11 varies as the line pattern goes far from the end of a cell array 18 into the interior of the array. The reason is considered that an exposure light irradiated onto the region without any patterns, namely, onto the vicinity of the cell array 18, has leaked out into the interior of the cell array 18 due to scattering in a projection optical system.
In order to manufacture highly reliable semiconductor devices, fine patterns must be formed as designed. It is desired for the line patterns 11 to be formed as originally intended as to the line-width and length thereof and uniform within the entire pattern.
When fine patterns are formed, influence from the surroundings of the patterns is not only from the effect of micro-flare. For example, there is a lot of such pattern formation processes that the transfer medium on which fine patterns are formed has certain unevenness in the surface, steps for instance, due to the influence of the undercoat thereof which has already been existing at the time of the pattern formation process. One of the examples is such a manufacturing process that a photolithography process is performed by further applying a photoresist onto a patterned polycrystalline silicon film which has been deposited on an oxide film. In such a situation, the photoresist film, which is a transfer medium for fine patterns, cannot have a smooth surface, but have an uneven surface, and is processed through each step of light exposure, etching, and development.
Further, it is likely that when regions from which a photoresist is removed is concentrated at a certain limited area, chemical substance formed through the reaction of the photoresist with a developer flows out in a small quantity into a surrounding in the process of development, or etching of the photoresist, resulting in undesirable influence on fine patterns to be formed in the surrounding of the area.
The influence from surroundings due to micro-flare, etc. is a very significant problem. For example, Japanese Patent Application Laid-Open No. 2003-100624 discloses a method for examining the effect of occurrence of flare due to an exposure apparatus. It is reported that the method includes preparing a photomask on which a plurality of fine line patterns with a line-width of 150 nm are spaced 150 nm apart; transferring the pattern on the photomask onto a photoresist by a photolithography process; and measuring a line-width of each fine line pattern for all the transferred line patterns, based on the knowledge that the line-width after the transfer will be changed if flare had occurred.
However, in such a conventional method, it takes a lot of time and labor to measure every line-width of fine patterns and thus the method is particularly inefficient in the development of new semiconductor devices where efficiency is required. Additionally, errors could be relatively large in each measurement of fine patterns.